This invention relates to power-supply apparatus in which modular energy generators such as fuel cells, solar cells, magnetic hydrodynamic generators and the like supply commercial quantities of electrical power in relatively large blocks to a power distribution system. This invention has particular relationship to apparatus in which the energy-generator modules have different outputs and are interfaced with the terminals through which power flows to the distribution system so that the outputs of the generators are appropriately consolidated. The problem presented by energy-generator modules which have different outputs is frequently encountered. Some of the modules in an installation may require replacement by new modules while others still have a useful life. In this case the new modules have a higher output than the old modules. The demand that modules have equal outputs imposes strict and difficult tolerances on the manufacture of the modules, materially increasing their costs. Interfacing which permits the use of modules of different outputs without substantial loss of power permits relaxation of strict tolerance and reduction in cost. A like problem arises where, as is usual, modules are connected in series-parallel arrays. Low efficiency, high resistance or short circuits in individual modules force other modules to alter their outputs and to operate at less than their optimum efficiency so that output voltages of all parallel strings of series modules are maintained equal.
The energy generator modules supply direct current that is converted into alternating current which flows into the distribution system. Typically a single common inverter is provided between the modules and the distribution system. It has been proposed, in an effort to solve the problem raised by the unequal outputs of the modules, to interpose several small inverters between the modules and the distribution system. Another solution is to provide DC-DC converters between the modules and a common inverter. Such solutions are costly.
Another expedient for solving the problem in the case of fuel cells is to vary the flow of the fuel gas, usually hydrogen, and/or the oxidizing gas, usually oxygen, to the cells of the different modules. This expedient demands a complicated gas-valve arrangement and is also costly.
Dickey discloses a protective circuit interfaced between fuel-cell generator modules and the terminals connected to the distribution network through an inverter. In this circuit the modules are connected in parallel through diodes to a DC bus, which in turn is connected to the inverter. Each module automatically adjusts its output current to match the DC bus voltage in accordance with voltage-current curves determined by module fuel and oxidizer pressure, temperature and flow relationship. The individual module efficiencies of the fuel cells are held within acceptable limits by a control system which adjusts module parameters as required. While it is contemplated that the apparatus disclosed by Dickey will operate satisfactorily, it is desirable that the efficiency of operation of the energy-generator modules be substantially improved. It is an object of this invention to provide power supply apparatus in which a plurality of modules of energy generators, such as fuel cells, provide large blocks of power to a distribution network, which apparatus shall include a network interfaced between the modules and the distribution network which network shall operate electrically rather than mechanically to consolidate the outputs of the modules so that they supply their individual power increments with high efficiency. Stated another way, it is an object of this invention to provide power-supply apparatus including a plurality of DC sources or modules supplying a distribution system in parallel and consolidated so that each module or parallel branch produces power at its maximum efficiency even though the branch output voltages at maximum efficiency are unequal.